Pathogenicity of Aeromonas spp. in carp polyculture systems in the central valley zone of Assam, North-east India

The present study was undertaken to find the incidence of motile aeromonas septicemia (MAS) in the freshwater aquaculture system in three districts viz. Nagaon, Morigaon and Sonitpur of Assam. A total of 293 ponds of varying size were surveyed during the disease outbreak and thirteen different diseases were recorded. For the first time, the study of severity of MAS in freshwater aquaculture system of Assam was undertaken and characterisation of Aeromonads was done through biochemical and molecular studies. Aeromonas hydrophila, Aeromonas veronii and Aeromonas sobria were detected from diseased fishes, with A. hydrophila being the most dominant species (51.64%) followed by A. veronii (21.97%) and A. sobria (18.68%). Pathogenicity studies through experimental infection of Labeo rohita with these isolates resulted in similar clinical signs as those exhibited by the diseased fishes collected from the farm during the outbreak. LD50 (lethal dose) doses estimated for A. hydrophila, A. veronii and A. sobria through probit analysis indicated that 50% mortality was noticed at 10-7.008, 10-8.034 and10-8.213, respectively for A. hydrophila, A. veroniiand A. sobriawith 95% CI (class interval). Keywords: Aeromonads, Histopathology, Labeo rohita, LD50, Motile aeromonas septicemia (MAS), Pathogenicity